1. Field of the Invention
The present invention relates to a liquid container that almost completely and stably supplies a liquid such as ink to a printing unit such as pen and print head. The invention also relates to a liquid using apparatus, a printing apparatus, and an ink jet cartridge.
2. Description of the Related Art
As a liquid using apparatus, such as an ink jet printing apparatus that applies liquid ink to a print medium from an ink jet print head to form an image on the print medium, a variety of types are in use. Some form an image by moving a print head relative to a print medium and at the same time ejecting ink from the traveling print head; and others form an image by moving a print medium relative to a stationary print head and at the same time ejecting ink from the stationary print head.
As for a method of supplying ink to a print head, which can be applied to these ink jet printing apparatus, there are an on-carriage system and a tube supply system. The on-carriage system has an ink tank mounted either inseparably or disconnectably to a print head so that the print head reciprocally travels together (in a main scan direction) carried on a carriage, with ink directly supplied from the ink tank to the print head. In the tube supply system, the ink tank is installed stationary at a separate position in the printing apparatus from the print head mounted on the carriage, with ink supplied through a flexible tube connecting the ink tank and the print head. This tube supply system includes a construction in which a second ink tank functioning as an intermediate tank (sub-tank) between the ink tank (main tank) and a print head is mounted on the print head or the carriage to directly supply ink from this second ink tank to the print head.
In these ink supply systems, the ink tank for directly supplying ink to the print head is provided with a mechanism that generates an appropriate level of negative pressure in a range which forms meniscuses in ink ejection portions of the print head to prevent ink leakage from the ink ejection portions and still allows for ink ejecting from the print head.
IN one example of such a negative pressure generation mechanism, a porous member such as sponge in which soaks and holds ink is installed in the ink tank to generate an appropriate level of negative pressure by its ink holding force.
In another example, ink is filled in a bag member formed of a material, such as rubber, that has an elastic force and generates a tension that tends to expand its volume, to create a negative pressure in the ink contained therein.
In still another example, a bag member is formed of a flexible film and a spring or the like which urges the film in a direction that expands a volume of the bag member is joined to an inside or outside of the bag member to generate a negative pressure.
In either of these mechanisms, however, the negative pressure tends to increase as the ink volume remaining in the ink tank decreases. When the negative pressure exceeds a predetermined level, ink can no longer be supplied stably to the print head. This gives rise to a problem of the ink tank becoming unfit for use before the ink in the ink tank is completely consumed.
For example, Japanese Patent Application Publication No. 3-24900(1991) discloses an ink tank constructed in the form of a hermetically closed, resilient bag member which directly contains ink and can deform according to the volume of ink contained therein and which has a spring member installed therein. In this hermetic bag member (ink tank) disclosed in Japanese Patent Application Publication No. 3-24900(1991), the negative pressure (a difference between the inner pressure of the ink tank and the atmospheric pressure) basically depends on a spring force so as to keep a balance therebetween. Thus, as the bag member deforms as a result of ink consumption and the spring is compressed, the negative pressure in the bag member increases. As a result, the negative pressure may exceed an appropriate range that allows normal ink ejecting from a print head, making it impossible for adequate meniscuses to be formed in the ink ejection portions of the print head or to supply ink stably to the print head. In this case, the ink volume in the bag member cannot be completely used.
There is also an ink tank characterized by a bag member whose material and shape are properly chosen. The bag member contains ink and produces a negative pressure by itself, while becomes flat with no inner space remaining when the ink contained therein is completely used up. This kind of bag member, however, has a limitation on the shape. If an ink tank is constructed of a rectangular parallelepiped case for accommodating a bag member, the bag member, even when loaded with ink, does not assume a shape that perfectly fits in the case, degrading an ink containing efficiency with respect to an overall ink tank space. Even with this bag member, when the ink is about to be used up, the negative pressure is so high as to cause a degradation of performance in supplying ink to the print head or make the ink ejecting operation of the print head unstable.
To prevent the negative pressure from becoming excessively higher than a predetermined level, the following mechanisms have been proposed.
For example, Japanese Patent Application Laid-open Nos. 7-125240(1995) and 7-125241(1995) disclose a mechanism which comprises a hydrophobic film and a tube vent installed in a tank and a ball fitted in the tube and which takes air into the tank when an inner negative pressure increases. More specifically, in the construction disclosed in Japanese Patent Application Laid-open Nos. 7-125240(1995) and 7-125241(1995), a tube vent (boss) communicating an interior of the ink tank with the outside has a plurality of protruding ribs formed on its inner wall. A ball with an outer diameter smaller than an inner diameter of the boss is fitted inside the boss' ribs so that it is in contact with the protruding ribs, thus forming a roughly ring-shaped orifice between the ball and the boss. A size of this orifice is set so that a small amount of ink is held as a liquid seal in the orifice by its capillary attraction. The orifice is shaped such that when the negative pressure in the container approaches an allowable limit of the operation range of the print head, the negative pressure overcomes the ink capillary attraction in the orifice, breaking the liquid seal and allowing air to enter into the ink tank through the orifice.
Japanese Patent Application Laid-open No. 6-183023(1994) discloses another mechanism which comprises a plate with a hole and a plate with a protrusion, both arranged to face each other in an ink bag of resilient sheet, and a spring member arranged between these plates. When the ink bag contracts as a result of a reduction in the remaining volume of ink and the inner negative pressure exceeds a predetermined level, the mechanism causes the protrusion of one plate to fit into the hole of the other plate, thus separating the holed plate from the resilient sheet to allow air to be introduced into the ink bag. With this mechanism, after air is drawn into the ink bag, the holed plate and the resilient sheet are brought into intimate contact with each other, preventing an ink leakage by an ink meniscus or a liquid seal between them.
These methods disclosed in Japanese Patent Application Laid-open Nos. 7-125240(1995), 7-125241(1995) and 6-183023(1994), however, all require a plurality of parts in the air take-in portion, rendering the construction complicated.
Further, if a pressure in the container rises extremely high, as when ambient condition variations occur (e.g., atmospheric pressure fall and temperature rise) after air has entered into the container to some degree, ink may be pushed out of the container. Where the above constructions are applied to an ink jet print head, this phenomenon may result in an ink leakage through ink ejection ports and vent. If a liquid is contained in a bag member of a resilient sheet, some buffer effect may indeed be expected which absorbs a certain range of pressure rise by permitting an air volume expansion due to a pressure reduction, thus alleviating the inner pressure rise. This buffer effect, however, has a limitation.
The construction disclosed in Japanese Patent Application Laid-open Nos. 7-125240(1995) and 7-125241(1995) forms a hermetically closed system through a balance between an ink meniscus force (liquid seal) in a ring-shaped orifice and a negative pressure produced by a spring. Although the mechanical construction is relatively simple, it lacks stability in maintaining the hermetically closed system. That is, the liquid seal may be broken depending on various conditions, leading to a leakage of accommodated ink. These conditions include a pressure difference between the inside and outside of the container, a reduction in ink viscosity due to temperature rise, inadvertent impacts on or fall of the ink tank during handling, and an acceleration to which the ink tank is subjected during a main scan in a serial printing apparatus. Also, since the liquid seal is susceptible to humidity, such as dry air, bubbles may be introduced un-uniformly. As such, ink supplying performance of the print head and printing quality are degraded.
To eliminate these problems, the construction of Japanese Patent Application Laid-open Nos. 7-125240(1995) and 7-125241(1995) provides an inlet maze connecting to a boss. The inlet maze is considered to function as an ink overflow container and secure a humidity gradient. The provision of the inlet maze, however, complicates the construction. Further, since the other end of the maze-like path communicates with open air at all times, the ink unavoidably evaporates to some degree through this inlet maze.
There is another problem. When ink in the container is used up, outer air rushes in, eliminating the negative pressure in the container. At this time, the inrush air may cause the ink remaining in the print head to leak out of ink ejection ports or the ink remaining in the container to leak through the ring-shaped orifice in which the meniscus is no longer formed.
Further, in these conventional mechanisms, an opening is provided in the ink tank to directly introduce the atmosphere. When ink in the ink tank is almost running out and a volume of air in the ink tank is larger than that of ink, the introduction of outer air into the ink tank to eliminate the negative pressure may render the maintenance of meniscuses in the ink ejection ports of the print head and in the opening (vent) of the tank incomplete, depending on the size and location of the opening. This in turn may cause an ink leakage and render the introduction of outer air incomplete.
Additionally, depending on a variety of conditions
a pressure difference between the inside and outside of the container, temperature variations, impacts on and fall of the ink tank during handling, and, in a serial printing system in particular, an acceleration to which the ink tank is subjected during a main scan
the liquid seal in the opening may be broken, resulting in an early introduction of air before the inner pressure reaches a predetermined level or, conversely, a leakage of ink. These conditions change depending on the design of the print head and ink tank and a physical property of ink. It is therefore necessary to optimize the shape, dimension and other designs of the opening and a basic construction of the negative pressure generation mechanism according to a usage of the container.
In addition to these inherent problems, the ink tank using the liquid seal for air introduction has another problem of reducing a degree of freedom of design in the printing apparatus.
That is, it is difficult to form the liquid seal portion separate from the ink tank as required when the liquid seal portion is arranged to be removable from the ink tank. If the liquid seal portion is formed separate from the ink tank, when it is directly mounted on the ink tank or indirectly connected to the ink tank through a tube or the like, complex processing or a special construction considering a pressure difference between the inside and outside of the ink tank is required in order to form a good meniscus in the ring-shaped orifice.
Where the liquid seal portion is provided remote from the ink tank and connected to it through a tube, the tube needs to be filled with ink in order to form a meniscus in the liquid seal portion. The introduction of air through the liquid seal portion forces the ink in the tube back into the ink tank. Refilling the tube with ink after the air introduction requires as complicated a construction or processing as the one described above.
In the construction disclosed in Japanese Patent Application Laid-open No. 6-183023(1994), since air is introduced through a small clearance between a thin plate member and a resilient sheet, a capillary attraction produced by a liquid entering that clearance changes a force required to separate the thin plate and the resilient sheet. As a result, the negative pressure level at which the air introduction is executed may become unstable.
Further, when a pressure of gas (air) in the container increases as the temperature increases, the resilient sheet must be deformed to virtually increase the inner volume of the ink bag to alleviate the increasing inner pressure. Therefore, the resilient sheet member is formed of an easily deformable material with a very low stiffness to provide a sufficient buffer function.
However, low stiffness materials used for such a resilient sheet generally have a small thickness and a high gas permeability, so air can easily pass through it into container due to gas osmolar pressure. Thus, if a liquid is stored in the container for a long period of time, a large volume of gas, so large as cannot be dealt with by a buffer function originally intended to absorb an expanded portion of gas (air) in the container, enters into the container, rendering the buffer function ineffective. It is therefore necessary to use a very expensive material deposited with a metal vapor to meet both of the requirements of a low stiffness and a low gas permeability.
Furthermore, to prevent an ink leakage and a diffusion of ink solvent when a printing apparatus is not printing, Japanese Patent Application Laid-open No. 2002-103642 discloses a construction in which a portion for introducing outer air into the container has a valve structure that can be opened and closed. In this construction, a valve disc is normally closed but, when the container is mounted on the printing apparatus, is opened to communicate the interior of the container with the atmosphere thus assuring a stable supply of ink to the print head. However, in this construction also, when the printing apparatus is not in use (particularly during transportation), the container may take any conceivable attitude, with the result that a liquid comes into contact with the air introduction valve to form a meniscus like a fluid seal, blocking the air introduction, or to form precipitates at the seal portion of the valve disc degrading a reliability of the valve disc operation.
Further, to secure a good sealing ability of the seal portion of the valve disc, the seal portion may be applied a highly viscous liquid such as grease or oil as a sealing material. This sealing material can provide a reliable seal even if the seal portion is scored or has an uneven or rough surface. But if ink is in contact with the seal portion, components of the sealing material dissolve into the ink, changing an ink composition, which will in turn render ink ejections unstable or cause the components of the sealing material in the ink to precipitate at the ink ejection ports, interfering with normal ink ejecting.
In yet another construction disclosed in Japanese Patent Application Laid-open No. 2001-310479, a container mounting lever is installed in a printing apparatus and provided with a valve mechanism which is operated by an external signal to control an opening and closing of an atmosphere introduction port in the container. In this construction, too, there are similar problems to those found in Japanese Patent Application Laid-open No. 2002-103642.
That is, in a construction in which a valve mechanism is provided at the atmosphere introduction port but in which a liquid can enter into the atmosphere introduction port, a liquid comes into contact with the valve disc depending on the attitude of the container or ambient condition variations (vibrations, temperature changes, pressure changes, etc.), degrading the reliability of the valve operation.
IN view of the foregoing, inventors were experienced to know that introduction of air into the liquid container is not preferably in order to eliminate the negative pressure in the container perfectly, whereas it is important to recover the negative pressure to a predetermined value. Also, the inventors determined, for achieving this, an amount of air to be introduced should be an adequate amount.
Particularly when a liquid container is used as an ink tank for directly supplying ink to an ink jet print head, the supply of ink at a stable flow velocity and in a stable flow volume is essential in enhancing a printing speed and image quality. To realize this, it is desired that a resistance which generates as it flows through an ink supply path be kept almost constant. It is therefore important to stabilize the negative pressure in the ink tank and keep it in a predetermined range. This requires components that introduce air into the ink tank to operate reliably.
The present invention has been accomplished with a view to overcoming the aforementioned drawbacks and is intended to realize at least one of the following objectives.
In a liquid container in which an containing portion for containing a liquid (e.g., ink) to be supplied to the outside (e.g., the print head) has a means for generating a predetermined level of negative pressure and an air introduction portion which can introduce air into the containing portion according to an increase in the negative pressure in the containing portion as a result of liquid supply to the outside and thereby maintain the negative pressure in an appropriate range, it is a first object of this invention to provide a construction that can prevent a liquid leakage from the air introduction portion under any environment of use and storage and that can maintain a stable negative pressure characteristic irrespective of a level of liquid consumption.
It is a second object of this invention to provide a liquid container (e.g., ink tank) which performs an introduction of outer air into the liquid container reliably and at an appropriate timing to keep the negative pressure in the container constant and thereby enhance the reliability for the negative pressure stabilization and which prevents a liquid leakage from a liquid supply port in the event of sudden ambient condition variations, ultimately eliminating a wasteful consumption of liquid. The second object also includes providing a liquid using apparatus (e.g., ink jet printing apparatus) using this liquid container.
It is a third object of this invention to provide an ink tank having a negative pressure adjust mechanism which can solve inherent problems of the above-mentioned ink tank using a liquid seal and which can enhance a freedom of design of a printing apparatus. The third object also includes providing an ink jet print head using the ink tank, an ink jet cartridge having the ink jet print head and the ink tank as a unit, and an ink jet printing apparatus with the ink tank.
It is a fourth object of this invention to provide a construction that opens and closes the atmosphere introduction port with a valve disc and which keeps a seal portion of the valve disc out of contact with the liquid to further enhance the sealing performance of the valve disc and assure a stable atmosphere introduction operation and high reliability, whatever attitude the container may take or whatever ambient condition changes may occur.